Water pollution - APPSC G1 Mains - Paper 4

(1) Sewage and other organic wastes—Sewage is the water borne wastes derived from both home and organic industries (slaughter houses and food processing plants). It includes human excreta, animal excreta, paper. cloth, soap, detergents, etc. The primary effect of stream pollution by sewage and other organic wastes provides large amount of food for decomposer organisms, mainly bacteria and fungi.

(2)Industrial effluents—A wide variety of both orga­nic and inorganic pollutants are present in effluents from breweries, tanneries, dying textiles, paper and pulp mills, steel industries, mining operations, etc. The heavy metals released by the industries are very fatal to the ecosystem.

(3)Agricultural discharges—Different chemical agents are used as artificial fertilisers and biocides (pesticides, herbicides, fungicides, nematocides, etc.). These discharges reach into the water bodies from agri­cultural fields.

(4)Acid rains—Acid rain pollutes aquatic ecosys­tems by changing the pH of water and affects the activities of aquatic flora and fauna.

(5)Waste heat—Water is used as coolant in genera­tors of electrical generating plants (both conventional and nuclear) as well as in various industries. Hot water is released to streams or lakes. The addition of such waste heat to water may perturb the aquatic ecosystem.

(6)Ground water—Important sources of ground water pollution are sewage and other pollutants from septic tanks, soak pits, refuse dumps, branyard manures, etc. especially in areas with high water table.

(7)Oil spill—In marine water the most serious pollu­tant is oil. A spill in oil or petroleum product due to acci­dent or a deliberate discharge brings about pollution. Off­shore exploration of petroleum also causes oil spills.

(8)Radioactive wastes—Various radioactive waste materials from nuclear reactors, mines and drop outs from scientific laboratories are generally packed within large containers and dumped into the deep sea. These radio­nuclides create pollution hazards.

Causal Agents of Water Pollution

Various substances are also responsible for water pollution. These are as follows—

(1)Pathogens—Various bacteria and viruses as well as protozoa derived from human excreta and other sewage sources cause various diseases to human and other animals and degrade the potability of drinking water

(2)Organic matters—Various organic compounds and their oxidative degradation processes in water cause water pollution.

(12)Radio nuclides—The nuclear power plants pollute environment with long life radioactive wastes that follow biogeochemical pathways and ultimately find their way into the ocean. They may remain in solution or precipitate chemically and get fixed in sediments. The radioactive elements in solution have the potential to accumulate in food chain. Various radionuclides viz., cerium, polonium, radium, strontium, uranium, etc., are involved in this process.

Water pollutants cause serious problems to human health as well as plant growth. They cause several envi­ronmental problems like biomagnification, eutrophication, oxygen depletion, degradation of physical and chemical property of water, etc.

Most of the agricultural discharges are extremely persistent chemicals and are not broken down quickly. Often these chemicals enter into the ecological food chain through some organisms which can accumulate them through a phenomenon called biomagnification. The most important substance to be biomagnified is DDT (Dichloro-diphenyl-trichloroethane). Since once it is intro­duced into the environment it keeps on circulation for many years. The manner in which DDT accumulates in the food chain is very interesting. Consequently, when DDT is in or on the food eaten by a herbivore, it tends to be stored in the fat of the animal, rather than excreted. If the concentration of the pesticide in the plant is repre­sented as 1, a particular herbivore may eat 100 plants to stay alive and the concentration in the herbivore may build upto 100 times in comparison to the plant. In the same way a carnivore may eat 100 herbivores and the pesticide is magnified to something like 10000 times than that of the plant.

Certain chemicals released from agricultural dis­charges are with toxic effects on human health. Some of these pollutants are listed in the Table 2.

Domestic wastes and certain agricultural wastes (particularly fertilizers) which are rich in phosphates and nitrates are poured in adjacent water bodies. As a result the water bodies become highly productive which prefers growth of aquatic angiosperms and bloom of some algae and bacteria. Such problem of excessive nutrient load in water bodies is known as eutrophication.

Eutrophication results extensive growth of algae and decomposing bacteria which in turn consume oxygen for respiration. In this way oxygen is greatly depleted. More­over, algal blooms also release some toxic chemicals which kill fish, birds and other animals, thus water begins to stink. Depletion of oxygen in an aquatic body can be measured by BOD or biochemcial oxygen demand. BOD is taken as indirect measure of water quality. It is infact a measure of the amount of oxygen required by microbes while stabilising decomposable organic matter.

Hot water added to streams and water bodies may cause serious effects like early hatching as well as no hatching of fish eggs, change in diurnal and seasonal behaviour and metabolic responses of organisms, migra­tion of some aquatic forms, decrease in species diversity of subjected ecosystem, increase in BOD of water bodies, etc.

Fresh water as well as ground water pollution is directly related to poor quality of drinking water throughout the world. The permissible limit of various parameters present in drinking water are given below (Table 3). After continuous deposition into the ground or surface water bodies, toxic metals and chemicals may change potability of drinking water.

Control of Water Pollution

The following techniques are employed to control water pollution—

(13)Stabilization of the ecosystem—This is the most scientific way to control water pollution. The basic princi­ples involved are the reduction in waste input, harvesting and removal of biomass, trapping of nutrients, fish mana­gement and aeration.

(14)Reutilization and recycling of wastes—Various kinds of wastes may be recycled to beneficial products, e.g., urban wastes may be recylced to generate cheaper biogas and electncity.

{3) Removal of pollutants—Council of Scientific and Industrial Research (CSIR), New Delhi has devised the following techniques for successful removal of different pollutants from water. These are—

(1)Removal of ammonia by ion-exchange technique.

(2)Removal of mercury by using mercury selective ion-exchange resin.

(3)Removal of phenolic compounds by the use of polymeric absorbents.

(4)Removal of sodium salts by reverse osmosis.

(4)Phytoremediation—Certain plants can accumu­late a large amount of various toxic substances like toxic metals, chemical substances, radionuclides, etc. in their body. This type of recovery of hazardous substances from soil or ground water contaminated with pollutants by using plants may be helpful to control water pollution.

(4)Awareness campaign—Creation of public awareness about pollution may be fruitful to prevent water pollution.